The present invention relates to an air bearing assembly, and more specifically, an air bearing assembly used for processing or measuring flat substrates.
Flat substrates, such as glass substrates, may be checked for stress deformation after cutting or any other process that may affect the quality of the substrate on an air bearing assembly. The air bearing assembly is typically a singular piece of granite having a flat upper surface. The granite is usually very thick to ensure that a solid, stable, and flat platform is obtained. Typically, it is desirable to apply air pressure (or another fluid) or to create a vacuum pressure between the substrate and the upper surface of the air bearing assembly. The vacuum pressure and air pressure is delivered by a combination of air and vacuum holes placed throughout the air bearing surface assembly. The vacuum pressure and air pressure is used to secure the substrate (e.g., for testing purposes) or to float the substrate at a specified fly height above the air bearing assembly for the purposes of manipulation and inspection.
Air pressure and vacuum pressure are applied to the substrate via air holes and vacuum holes, respectively. The air and vacuum holes are arranged throughout the air bearing assembly to ensure proper fly height, as well as maintaining the flatness of the substrate. Without the vacuum holes, air pressure is more likely to build up at the center of the substrate because air provided via the air holes does not readily escape from between the substrate and the air bearing assembly. In contrast, air more easily escapes past the edges of the substrate. A buildup of air pressure at the center of the substrate causes bowing and deformation of the substrate. Vacuum pressure provided via the vacuum holes helps prevent the build up of excess air pressure at the center of the substrate. Thus, flatness of the substrate is controlled by maintaining even pressure across the entire surface of the substrate via the air and vacuum holes.
Typically, the air and vacuum holes extend through the entire thickness of the air bearing assembly, which again is very thick. Unfortunately, boring the air and vacuum holes through the entire assembly weakens the overall structural integrity of the air bearing assembly. Further, it is exceedingly difficult to bore a small diameter hole through a hard substance such as granite. Among the problems encountered with drilling such holes is the likelihood of the hole not extending in a proper axial direction (such as perpendicular to the flat upper surface of the granite), the holes being of improper cross-sectional shape (e.g., oval instead of circular), or the drill bit used to bore the hole being damaged. As the overall structural integrity of the air bearing assembly is important for maintaining a stable, flat upper surface of the assembly (e.g., to manipulate and process the substrate), the conventional surface assembly has not been entirely satisfactory.
Thus, there is a need in the art for an air bearing assembly that allows individual air and vacuum lines to be installed within the assembly without having to bore through the entire thickness of the assembly.